不能使用类型转换将通用类“新建对象”

Question

This code is for learning generic class and stack operation. but it has some error about declare variable type

package lab11_2_590510535;
import java.util.Scanner;

class Queue <TYPE>{
    private int count;
    private int front;
    private int rear;
    private int n;
    private Object [] item;
    private TYPE queueFront;
    static void pl(Object a){System.out.println(a);}
    static void p(Object a){System.out.print(a);}

Queue(int x){
    n = x;
    item = new Object[n];
    front = 0;
    rear = -1;
    count = 0;
}

public boolean isEmpty(){
    for(int i = 0 ; i<item.length ; i++){
        if(item[i] != null){return false;}
    }
    return true;
}

public boolean isFull(){
    if(item[item.length] != null){return true;}
    else{return false;}
}

public void enqueue(TYPE v){
    if(!isFull()){
        if(rear < n-1){
            rear++;
            item[rear] = v;
            count++;
        }
    }else{pl("Queue is Full.");}
}
public TYPE dequeue(){
    if(!isEmpty()){
        queueFront = item[front];
        front++;
        count++;
    }else{p("Queue is empty.");}
    return queueFront;
}
public void show(){
 for(int i = 0 ; i <item.length ; i++){
     if(item[i] !=  null){p(item[i] + ", ");}
 }
}


public class Lab11_2_590510535 {
    static void pl(Object a){System.out.println(a);}
    static void p(Object a){System.out.print(a);}
/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    // TODO code application logic here
    Scanner keyboard = new Scanner(System.in);
    char choice;
    int N;
    p("Enter N: ");
    N = keyboard.nextInt();
    p("Choice input type; int(1) , char(2): ");
    choice = keyboard.next().charAt(0);
    if(choice == '1'){Queue <Integer> q = new Queue(N);}
    else if(choice == '2'){Queue <Character> q = new Queue(N);}
    do{
        pl("1) enqueue"); pl("2) dequeue"); pl("3) show"); pl("4) exit");
        p("Enter function number : ");
        choice = keyboard.next().charAt(0);
        if(choice == '1'){
            p("Enter data: ");
            Object s = keyboard.next();
            q.enqueue(s);
        }
        else if(choice == '2'){Object s =  q.dequeue();
            pl(s);
        }
        else if(choice == '3'){q.show();}
    }while(choice != '4');

    }
}

1.After user input choice and I create generic object with type casting in do...while loop it can't find "q".

2.In public TYPE dequeue() method line "queueFront = item[front];" Object can't be convert to TYPE ,how can I fix it.

Answer 1

Try to change private Object [] item to private TYPE [] item . Also you will need to know how to create a generic array for your example: How to create a generic array? How to create a generic array in Java?

You will need to change item = new Object[n]; to item = (TYPE[]) new Object[n];

However you should avoid creating generic types and instead you should inject them or use a factory to create them.